An upflow water clarifier, such as those disclosed in Wyness U.S. Pat. Nos. 4,146,471 and 4,765,891, is a type of clarifier that has a prominent conical portion extending upwardly and outwardly from a central lower cylindrical end. Contaminated water enters the clarifier near the lower end. Inside, the water is given a rotational movement, often in part by feeding it into the clarifier in a tangential direction, resulting in a generally upward helical flow of the water within the clarifier.
The increasing diameter of the clarifier toward its upper end causes a decrease in velocity of the liquid as it moves upwardly. As the velocity decreases, suspended solids having a higher density than water agglomerate and separate from the water, forming a revolving sludge blanket that remains behind as clarified water continues moving upwardly until being withdrawn as clarified effluent.
Conventionally, the effluent is removed from the clarifier over weirs or troughs, while sludge is periodically removed through a sludge concentrator, which is typically located on the central axis of the clarifier, but which can alternatively be provided off of the central axis or even outside of the vessel, immediately adjacent the vessel wall.
One problem with upflow clarifiers is a limitation in the maximum practical size. In order to handle large flow rates, upflow clarifiers can become undesirably tall, leading to difficulties in maintaining structural stability and in fitting into an existing hydraulic profile. If the top of the clarifier is to be at ground level, more difficult and expensive excavation is needed; if the base of the clarifier is to be at ground level, more energy is needed to pump the liquid through the clarifier. Aesthetic concerns may also be a significant problem.
Use of multiple smaller vessels is often not a good solution. Multiple smaller vessels may be more expensive and may require more land than is readily available, and can also create piping and valving problems.